|Year : 2017 | Volume
| Issue : 2 | Page : 208-212
Modeling of lung cancer risk due to radon exhalation of granite stone in dwelling houses
Nuclear Science and Technology Research Institute (NSTRI), Tehran, Iran; University of Kyrenia, TRNC, via Mersin 10, Kyrenia; Near East University, Nicosia, North Cyprus, Mersin 10, Turkey
|Date of Web Publication||23-Jun-2017|
Nuclear Science and Technology Research Institute, Tehran, Iran
Source of Support: None, Conflict of Interest: None
Aims: Due to increasing occurrences of lung cancer, radon exhalation rates, radon concentrations, and lung cancer risks in several types of commonly used granite stone, samples used for flooring in buildings, have been investigated.
Subjects and Methods: We measured the radon exhalation rates due to granite stones by means of an AlphaGUARD Model PQ2000 in a cube container with changeable floor by various granite stones. The lung cancer risk and percentage of lung cancer deaths (LCRn) due to those conditions were calculated using Darby's model.
Results: The radon exhalation rates ranged from 1.59 ± 0.41 to 9.43 ± 0.74 Bq/m 2/h. The radon concentrations in the standard room with poor and normal ventilation were calculated 20.10–71.09 Bq/m 3 and 16.12–47.01 Bq/m 3, respectively.
Conclusions: The estimated numbers of lung cancer deaths attributable to indoor radon due to granite stones in 2013 were 145 (3.33%) and 103 (2.37%) for poor and normal ventilation systems, respectively. According to our estimations, the values of 3.33% and 2.37% of lung cancer deaths in 2013 are attributed to radon exhalation of granite stones with poor and normal ventilation systems, respectively.
Keywords: Annual dose, Darby's model, granite stones, lung cancer, radon
|How to cite this article:|
Abbasi A. Modeling of lung cancer risk due to radon exhalation of granite stone in dwelling houses. J Can Res Ther 2017;13:208-12
| > Introduction|| |
Radon is the gaseous radioactive product of the decay of the radium isotopes 226 Ra, from natural 238 U series, which is present in all terrestrial materials. The half-life of 222 Rn is 3.824 days and has four short-lived decay products:218 Po (3.05 min),214 Pb (26.8 min),214 Bi (19.9 min), and 214 Po (164 μs). Both polonium isotopes are alpha emitters. These radionuclides are the most significant contributors to human exposure to ionizing radiation from natural sources. This contribution accounts for 50% of the total annual human dose. The variations of the radon concentration in a building mainly dependent on the variations of the ventilation conditions and air exchange between outdoor and indoor. Granite is believed to have an average higher radon exhalation rate than other building material.,,, In addition, the average radon emanation value due to granite samples was reported to be about 21% of the total radium concentration. The main exposure of radon for most people in the world is radon entering the body through inhalation.,,,,, Most inhaled radon is decayed, and decay products are quickly deposited in the lung tissues, after which irradiate sensitive cells in the respiratory route cause the increased risk of lung cancer. Recent estimates of the proportion of lung cancer attributable to radon range from 3% to 14%, depending on the average radon concentration in the country.,,,, The Environmental Protection Agency reports that radon is the second major cause of lung cancer, after cigarette smoking.
In this research, the radon concentrations due to only granite stones were measured by means of an AlphaGUARD Model PQ2000. The radon exhalation rate, annual effective dose rate, and lung cancer risk were estimated in the studied area.
| > Subjects and Methods|| |
The radon concentration of the selected 21 samples of granite stones commonly used as decorations on floors in Iran was measured using special cubic chamber setup with the dimensions of 70 cm × 60 cm × 50 cm [Figure 1]. Each sample was put in a cubic setup and sealed to reach equilibrium between radon and its daughters. After equilibrium was reached, the radon concentration was measured using an AlphaGUARD Model PQ2000 PRO (SAMYM Co, GmbH). This detector operates based on the passing of Rn gas from a filter to the ionization chamber. The radon exhaled from granite stones was measured for 30 min, and each sample was measured in (n = 4–7) times to get the average concentration. The radon gas exhalation rate was computed by:
Where Ex is the Rn gas exhalation rate (Bq/m 2/h); A is Rn concentration activity (Bq/m 3); λ is decay constant of Rn; V is chamber volume (m 3); and F is the area of sample. To estimate the Rn concentration in a standard living room, a room with the dimensions of 4.0 m × 5.0 m × 2.8 m has been defined. In this room, the floor has been covered with granite stones. The steady state of Rn concentration in the room is given as follows:
Where Ci is Rn concentration in cubic; Co is the outside radon concentration with the world average value being 10 Bq/m 3 in the outdoor air; λv is the air exchange rate at time t in h −1, this value is 0.3/h for poor ventilation system and 0.5/h for normal ventilation systems.
The annual effective doses received from granite's flats in the center of the room were calculated using the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) model.
Where ED is annual effective dose in mSv/year; C (Rn) is weighted average radon concentration (Bq/m 3); Ef is the equilibrium equivalent radon factor (0.4 taken for indoors); Of for occupancy factor (0.8 according UNSCEAR 2000 report); T for time (8760 h/year); and Dcf is dose conversion factor (9 × 10−6 mSv/h per Bq/m 3). The resulting worldwide average of the indoor annual effective dose is 0.48 mSv, due to all the materials used in construction.
Assessment of lung cancer risk
The relation between indoor radon concentration and dose effect is linear as demonstrated by many epidemiological investigations. The integrated analysis on residential radon in 13 European countries is such investigations. In this statistical model, the results were based on a linear model for the relationship between the radon concentration and the risk of lung cancer. The mathematical expression is:
Where β is the proportionate increase in risk per unit increase in measured radon; x is measured radon concentration. The fitting model equation with 95% confidence is:
To estimate the number of lung cancer deaths due to indoor exposure from granite stones, we applied the following relation:
Where NRn, a is the number of lung cancer deaths due to indoor radon exposure in area a; NT, a is the total number of lung cancer deaths in area a, where the 222 Rn concentration was calculated. The percentage of lung cancer due to 222 Rn exhaled from granites (LCRn) could be estimated from the relative risk attributable to radon (RR) with the following formula:
Where LCRn is lung cancer due to 222 Rn (%) and is fraction of risk attributable to radon.
| > Results and Discussion|| |
[Table 1] shows the radon exhalation rates, radon concentration, and annual effective dose in both types of ventilation systems. These results are derived from granite stones that commonly used as decorations on floors in buildings. As shown in [Table 1], the radon exhalation rates mean is 4.79 ± 0.64 Bq/m 2/h. The minimum and maximum values of radon exhalation rate are simple GSI-6 with 1.59 ± 0.41 Bq/m 2/h and sample GSI-20 with 9.43 ± 0.74/Bq/m 2/h, respectively. In addition, in poor and normal ventilation systems, indoor radon concentration and annual effective dose mean are 15.37 Bq/m 3 and 0.39 mSv/year and 13.26 Bq/m 3 and 0.33 mSv/year, respectively.
|Table 1: The radon exhalation rates, radon concentration, and annual effective dose due to granite stones|
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The resulting RR values, based on Darby's model predications, in poor and normal ventilation systems, are 1.024 and 1.035 on average, respectively. The results of annual lung cancer deaths due to indoor radon exposure in area a (NRn, a) and the percentage of lung cancer (LCRn) due to radon concentration on average are shown in [Table 2]. In addition, the histogram of lung cancer (LCRn) value by granite samples is presented in [Figure 2].
|Table 2: The lung cancer risk (relative risk), number of lung cancer deaths (NRn,a), and the percentage of lung cancer deaths (LCRn) due to granite stones (according to the latest WHO data published in April 2013 lung cancers deaths in Iran)|
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|Figure 2: Histogram of lung cancer deaths (LCRn) due to various granite stones|
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The numbers of lung cancer deaths attributed to radon exposure due to granites, based on Darby's model (Eqs. 4–7), for lifetime nonsmokers are 103 and 145 deaths from 4356 deaths in 2013. In the same manner, we calculated the percentage of lung cancer deaths (LCRn) as 3.33% and 2.37% for poor and normal ventilation systems, respectively. The comparison histogram of annual effective dose due to granite floors with poor and normal ventilation systems against to worldwide inhalation radon dose (0.2–10 mSv/year) is shown in [Figure 3]. As well as, the lung cancers attributed to radon-exhaled granites to worldwide range in building materials (3%–14%) are compared in [Figure 4].
|Figure 3: The worldwide inhalation radon dose rates and standard room with poor and normal ventilation systems|
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|Figure 4: The worldwide range of annual lung cancer due to building materials and standard rooms with two mood ventilation systems|
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The results of the current estimates for radon concentration and lung cancer risk are compatible with other reports such as lung cancer deaths attributed to indoor radon exposure in 13 European countries (8.44%), in France (2.2%–12.4%), the North American studies (11%), and the USA (10%–12%).
| > Conclusion|| |
The radon exhalation rate, radon concentration, and annual effective dose magnitude were calculated in granite stones commonly used in Iran. The results showed that the 222 Rn exhalation rate Ex value ranges are 1.59 ± 0.41–9.43 ± 0.74 Bq/m 2/h, with an average of 4.79 ± 0.63 Bq/m 2/h. These obtained values are to be compared with other reported results in Saudi Arabian  and Brazilian  granites: 0.41 ± 0.13–10.6 ± 1.4 and 0.60 ± 0.10–21 ± 2.3 Bq/m 2/h, respectively.
The radon concentration in two states of poor and normal ventilation systems are 11.62–20.80 Bq/m 3 and 10.98–16.54 Bq/m 3, respectively. The annual effective dose mean values are 0.39 mSv/year in poor state and 0.33 mSv/year in normal state. The worldwide radon effective dose values are between 0.2 and 10 mSv/year with an average 1.15 mSv/year. According to the International Commission on Radiological Protection recommendation, annual effective dose limit for an individual member of the public is 1 mSv/year. Therefore, we receive 30% of annual effective dose limit using the granite stone. Based on Darby's model, the results of lung cancer deaths (LCRn) attributed to radon exposure due to granites are 3.33% and 2.37% for poor and normal ventilation systems, respectively. According to the WHO reports in 2009, the worldwide range of lung cancer related to radon causes are between 3% and 14% of all lung cancers. Therefore, the estimated model results in this investigation are compatible with the WHO reports.
This work was carried out between the Union's Commercial Granite Stones of Iran (UCGSI) and the Eastern Mediterranean University. The authors are very grateful to the cooperation and support of management and staff of UCGSI.
Financial support and sponsorship
The financial support was provided by the Science and Technology Research Institute of Iran.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]